The present invention relates to an apparatus for winding successive convolutions of one or more continuous strands of material onto a selected workpiece. More particularly, it concerns an improved apparatus for winding strands of wire onto ring-shaped articles, such as toroidal cores. As used herein, the term "core" means a ring-shaped article having the plane closed curve cross section of a toroid, or any one of various other different cross sections. The term "wire" as used herein means any material in the form of a flexible strand which is not so supple that it buckles easily when pushed from one end in a length-wise direction. The terms "continuous wire supply" and "continuous wire source" mean that the length of continuous wire in the supply coil or source is sufficiently long to enable a plurality of cores to be wound from the supply or source before the wire is used up. As used herein the term "oval-shaped" refers to a closed curve formed from two semicircular curves of equal radius connected by two straight-line segments of equal length.
Wire wound ferrite cores have been used as electronic components for many years. They are particularly adapted for producing a gapless magnetic field. Inductance coils and transformers can be constructed in this manner. Rheostats can be constructed with cores wound with resistance wire. Very small wire wound cores have also been used as memory elements in computers.
Heretofore, the wire has often been wound onto such cores by hand. This process is time consuming and tedious and frequently results in inferior coils due to non-uniform spacing of the wire turns around the core. More recently, the wire has been wound onto such cores through the use of a rotating winding ring or shuttle which carries several loops of wire and rotates at high speed through the central aperture of the core. U.S. Pat. No. 2,810,530 discloses an exemplary apparatus for winding cores in this manner. Such apparatus require the constant attention of an operator who must mount each core, manually wind the appropriate number of loops of wire about the shuttle, and remove the core from the shuttle upon the completion of the winding operation.
Improved winding apparatus have been developed which do not require the insertion of a winding ring or shuttle, or any other element through the central aperture of the core. Instead, a coil of wire is formed which extends through the central aperture of the core. Individual turns about the core are made from the loops of the coil during continuous rotation of the coil. One such apparatus is disclosed in U.S. Pat. No. 3,132,816. In that apparatus, loops of wire are apparently held frictionally between the engaging faces of two ring-like belts which are rotatably driven about their central axes. The wire loops pass through the center of a core supported between separated portions of the belts. The trailing end of the wire is rigidly held so that as the coil rotates the wire loops are wound into turns about the core.
Finally, U.S. Pat. No. 3,985,310, owned by the assignee of the present application, disclosed a superior shuttleless core winding apparatus invented by the Kent brothers. A length of wire is fed into a radially inwardly facing annular channel through a curved feeding tube. The wire is propelled around the channel by two pairs of driven pinch rollers to form a number of radially spaced circular loops. The upper and lower boundaries of the channel maintain the loops in a single concentric layer. A gap is provided in the channel for receiving the core so that as each circular loop is formed, the wire in that loop passes through the core opening. When enough wire has been fed the trailing end of the wire is held. The circulation of the loops through the core opening continues and each loop is wound into turns about the core, one new turn being completed for each circulation of the loops around the annular channel. The winding of two or more wires simultaneously around the core (known as bifilar and multi-filar winding) can also be accomplished with the Kent brothers apparatus.
It is believed that the Kent brothers' apparatus of U.S. Pat. No. 3,985,310 represents the best prior art device for high speed manufacture of wire wound cores. However, this apparatus has certain limitations. Because the wire loops are formed into a single concentric layer within the circular channel, provisions must be made to insure that each loop is driven around the channel at an angular velocity which is equal to or greater than that of any loop radially outwardly of it. If the angular velocity of any inner loop were less than that of any outer loop, the inner loops would circulate around the channel more slowly and would get larger and jam against the outer loops, preventing proper winding of the core. To avoid this result, the driven pinch rollers are not cylindrical but instead are bevelled and supported at an angle to each other as illustrated in FIG. 3 of the patent. Roller wear and imprecise positioning of the rollers can result in an improper speed relationship between the concentric wire loops, and this will often terminate the winding operation.
Furthermore, the loop capacity of the Kent brothers' apparatus is relatively small and this places an upper limit on the number of turns that can be wound around the core. If too many loops are formed within the channel of the apparatus, it is difficult to maintain the required radial speed relationship. This often results in jamming or buckling of the loops. Finally, the Kent brothers' apparatus is well suited for winding the cores with smaller wire such as 31 to 38 gage. The winding of larger cores with heavier gage wire, for example 12 gage wire, requires considerably greater operative tension. The opposing pairs of driven pinch rollers are not well suited for providing sufficient positive driving force to enable heavier gage wire to be wound around larger cores. Winding with heavier wire also requires positive guidance of the wire on both its inner and outer boundaries as the loops are formed and circulated. In the Kent brothers' apparatus there is no inner boundary guidance.